1. Field of the Invention
This invention generally relates to the field of subterranean well completions and controlling flow of production fluid from wells comprising primary and lateral wells.
2. Description of the Related Art
In many instances, a hydrocarbon producing wellbore includes not only the primary well drilled into a subterranean formation, but also one or more lateral wells extending into the surrounding formation adjacent the primary wellbore. FIG. 1 provides a cross sectional view of an example of a wellbore production system 10 installed in a wellbore having lateral wells. In this example, the primary wellbore 5 extends from the surface and into a producing zone within a subterranean formation 6. The associated casing 7 cemented within the wellbore 5 extends substantially along the entire length of the wellbore and also into the formation 6. Perforations 11 formed through the side of the wellbore 5 and through the casing 7 into the surrounding formation 6 provide fluid pathways for production fluid (hydrocarbon gas and liquid) to flow into the wellbore 5. The wellbore production system 10 includes completion tubing 13 coaxially inserted within the casing 5. The completion tubing 13 extends along the length of the wellbore 5 up to the wellhead 14 and delivers the production fluid therein to the wellhead for distribution to a production line 16.
In addition to the production fluid from the subterranean formation 6, the lateral wellbores (3, 4) extend into corresponding production zones within corresponding subterranean formations (8, 9). These lateral wellbores (3, 4) also include perforations 11 providing fluid communication between the wellbore and their associated formation. In the embodiment of FIG. 1, the produced fluids from the primary wellbore 5 and the lateral wellbores (3, 4) are deposited into a single completion tubing 13 where these fluids are mixed. It should be pointed out that other configurations exist wherein dedicated tubing is provided to each production zone thereby preventing commingling of fluids within the wellbore 5. One disadvantage of installing dedicated tubing is the presence of additional hardware within the wellbore as well as the difficulty of introducing and maintaining the hardware in these individual circuits.
The producing zones (6, 8, 9) may operate or produce at varying pressures. To prevent an imbalanced pressure situation within the completion tubing 13, chokes (18, 20, 22) are provided in the fluid flow pathway between the respective producing zones and the completion tubing 13. Chokes provide a regulating effect on the fluid by adjusting the flow rate and pressure to compensate for pressure differences between these different producing zones. Also shown in FIG. 1 are packer seals 26 proximate to the junctions between the primary wellbore 5 and the laterals that seal the flow pathway between the annulus between the tubing 13 and casing 5 and forces fluid flow through perforations 24 in the tubing string 13 and through the respective chokes (18, 20, 22).
While existing chokes, or other flow control mechanisms regulate or adjust fluid flow and fluid pressure, these devices do not limit flow direction therethrough. Accordingly, in situations wherein pressure within the production tubing 13 may exceed pressure within a particular lateral wellbore or its associated producing zone, the fluid in the higher pressure tubing string may migrate into the production zone through any one of these known devices. This situation could occur if a flow regular of a high pressure producing zone fails or if the well is suddenly shut in and the respective valves are not closed prior to the shut in. Because migration of producing fluids from one zone into another zone having a different pressure may cause deleterious effects on the lower pressure formation, this is an undesired situation. Therefore, it would be advantageous to develop a device for preventing the cross flow of production fluids from producing zones having different pressures. It would also be advantageous to develop and implement a device that can regulate flow in addition to preventing cross flow of production fluids.